Tire air pressure switch



Dec. 12, 1939.

E. C. HENDERSON TIRE AIR PRESSURE SWITCH Filed July 14, 1957 1N VENTOR.

Patented Dec. 12, 1939 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to alarm systems for indicating the drop of pressure in a pressure containing medium, and consists in the combination, construction, and arrangement of parts hereinafter described and claimed.

An object of the invention is to provide an alarm system in which means is provided for selecting the minimum of pressure below which the alarm shall be actuated.

Another object of the invention is to provide an alarm system particularly adapted to indicate the drop 0f pressure of air in a tire by means of an audible or visible alarm signal.

A further object of the invention is to provide 1D an alarm system for indicating the drop of pressure in a tire, in which the toggle joint is employed to actuate the signal means.

A still further object of the invention is to provide a device which is extremely simple in 2.0 construction and which is durable and efficient for the purpose intended.

Other objects and advantages will appear as the specification proceeds and the novel features of the device will be particularly pointed out in .25 the claims hereto annexed.

In the accompanying drawing:

Fig. 1 is a section through a portion of a tire rim having a device thereon constructed in accordance with the teachings of my invention.

.30 Fig. 2 is a central cross section through the device showing the parts in different position from that shown in Fig. l.

Fig. 3 is a side View of Fig. 2. Fig. 4 is a cross section of the device taken on 35 the line 4-4 of Fig. 2.

Fig. 5 is a wiring diagram.

In general terms my invention comprises a hollow casing having a piston arranged within the casing and communicating with the pressure 40 subjected medium. A spring pressed toggle joint is arranged in connection with the piston, which joint is adapted to shift its position whenever the pressure in the medium falls below a certain selected minimum and thereby to engage an 45 alarm switch.

In detail, Fig. 1 shows a portion of a conventional automobile Wheel I having a rim 2 carrying a pneumatic tire 3 and tube 4. A brake drum 5 is also carried by the wheel I which is 50 closed by a stationary brake dust shield 6. To

the latter is attached a bracket 8 which adjustably supports a switch 9 on the end thereof. As shown in Fig. 5, the switch 9 consists of two parallel side plates I0 and an elongated central blade 55 II insulated therefrom. 'I'he latter is connected (Cl. D- 58) to a push button switch I2 which is connected with a signal I3 such as a horn, a light, or the like. A wire I5 connects the signal with a battery I6 which in turn is connected with the side plates I0. It will be readily understood that whenever the blade II is deected from its normal position and contacts one of the side plates i, an electric circuit is thus established which will energize the signal I3.

My invention consists of a device to actuate the switch 9 whenever the pressure in a tire drops below a certain preselected minimum. The device consists of a cylindrical hollow casing 20 having a conical flange at one end thereof which snugly ts a conical opening 22 in the rim 2, and by means of which the casing is removably retained by the latter. A piston 23 is slidably arranged in the end of the casing 20 adjacent to the rim 2, said piston being formed with a flat head 25 protruding inside of the rim and contacting the tube 4, the pressure of air in which20 forces the head 25 against the casing 20. The opposite end of the piston is flared out to prevent its removal from the casing 20 and has a central conical depression 21 formed therein, the purpose of which will be hereinafter fully de- 25 scribed.

The other end of the casing 20 is internally threaded and closed by a plug having a ange 32 on the outer end and a centrally located conical depression 33 in the inner end thereof. The 30 casing 20 is formed with two opposite slots 34 extending through said casing. Disposed within said casing the lever 35 has a cone-shaped leg 38 dependent therefrom which projects into the depression 2'I in the piston 23 and rests on the 35 bottom thereof. As the depression 2'I is' wider at its top than the leg 38, the lever 35 is free to swing about the lowermost point of said leg from the position shown in full lines to that shown in dotted lines in Fig. 1.

The lever 35 is also formed with a conical depression 39 about the leg 38 in which one endof a pin 40 rests, the other end of said pin 4l! being confined in the depressions 33 of the plug 3D. The outer diameter of the depressions 38 and 33 45 is larger than the diameter of the pin 40, therefore the latter also has freedom to swing therein.

A washer 42 is interposed between the ange 32 of the plug 30 and the end of the casing 2D and has a lip 44 bent upon itself which is adapted to enter one of the slots 34. The washer 42 is also made with an extension 46 between which and the end 3l ofl the lever 35, an expansible coil spring 4l is interposed, to urge said extension upwardly against the ange 32. The extension 46 carries an embossment All which is adapted to enter one of several notches i8 cut in the flange 32. The spring lll forces the embossment lll into a notch 48 and swings the lip l downwardly into registry with the slot 34, thus locking the plug 32 and the casing 2i) together.

It will be noted that the pin ill and the leg of the lever 35 constitute a toggle joint conn-ned between the plug 3Q and the piston 23. The spring 4'! urges the end 3? of the lever 35 downwardly into an operative position, as shown in Fig. l in dotted lines. In order to shift the lever into the dotted position, it is necessary for the toggle joint to pass through a dead center position as shown in Fig. 2. That is, when the center lines of the pin :it and the leg 38 form a straight angle, it is necessary to force the piston Z3 outwardly against the pressure of air in the tube. This may happen only when the pressure of the spring all overcomes the resistance of pressure in the tube il.

The air pressure in the tub-c, which should be overcome by the pressure of spring il? and thus cause the toggle joint to shift, may be selected by changing the position of the plug The further said plug is moved away from the piston 23 the closer is the angle formed by the center lines of the pin il@ and leg to a straight angle, and therefore the greater pressure in the tube l will be required to prevent the toggle joint from shifting. rThe closer the plug Si and the piston 23 are, the smaller is the obtuse angle formed by the center lines o pin and leg, and the greater effort is required to overcome it. Consequently the lesser pressure in the tube fl will be required to prevent the toggle joint from shifting. Therefore by adjusting the plug 32 in the casing 2li, the minimum pressure which is neces-- sary to prevent the toggle joint from shifting may be carefully selected.

After the lever 35 has been shifted into an operative position, as shown in Fig. l. in dotted lines, the end 3l thereof will strike the blade il of the switch Il with every revolution of the wh eel l, causing it to Contact one of the side plates E5, thus intermittently energizing the signal I3 as has been previously stated. A. driver being informed that deflation is taking place in one of the tires, may, by pressing the push button notch I2, stop the signaling.

Additional air may be introduced into the tire and the device may be set in operative or cocked position (sho-wn in full lines in Fig. l). rEllis may be accomplished by pressing the end 3S of the lever 35 downwardly.

While I have, for the sake of clearness and in order to disclose my invention so that the same may be readily understood, described and illustrated as applicable to a pneumatic tire, I desire to have it understood that this invention s not limited to this particular application, but may be advantageously applied in many other cases.

Having thus described this invention, what l' claim and desire to secure by Letters Patent is:

l. lin an alarm system for indicating the cleliation of a pneumatic tire below a preselected minimum, comprising in combination a wheel having a rim carrying a pneumatic tire and a tube therein, a hollow casing aflixed to the rim; a piston slidably carried by said casing and abutting the tube; a lever extending transversely through said casing and having an arm on one side thereof fulcrumed on said piston; a pin fulcrumed between said lever and a closed end of said casing at a point opposite the arm on said lever, said lever and pin being held in open position when the pressure of air in the tube is above a preselected minimum and adapted to be shifted into a diierent position when the air pressure in the tube drops below said minimum; and a spring to urge said lever to shift its position as well as the position of the fulcrum pin.

2. in an alarm system for indicating the deflation of a pneumatic tire below a preselected minimum, comprising in combination a wheel having a rim carrying a pneumatic tire and a tube therein; a hollow casing affixed to the rim; a piston slidably carried by said casingand abutting the tub-e; an adjustable plug carried by the other end of the casing; a lever extending transversely 'through said casing and having an arm on one side thereof fulcrumed on said piston; a pin fulcrumed between said lever and the plug in the closed end of the casing at a point opposite the arm on said lever, said lever and pin being held in open position when the pressure of air in the tube is above the preselected minimum.' and adapted to be shifted into diiierent position when the air pressure in the tube drops below said minimum; and a-spring to urge said lever to shift its position as well as the position of the fulcrum pin; and means for adjustingthe position of the plug in the casing.

ELDON C; HENDERSON. 

